Concerning display panels for projectors, the technologies have made rapid progress due to market demands, design improvements, improved manufacturing methods or the like, and because of pixel micronization, display panels that feature high definition and miniaturization have been developed.
Among recent projectors, projectors having high-definition display panels such as, for example 4K-compatible projectors have also appeared. Herein, the 4K-compatible projector is a projector that includes a display panel having a pixel count of 4K×2K (e.g., 3, 840×2, 160 pixels or 4,096×2, 160 pixels).
On the other hand, technologies have been proposed that can increase the number of pixels on the projected image without using high-definition display panels.
For example, Patent Document 1 discloses a projection display device that can produce a projected image whose number of pixels is twice as many number of pixels of the display panel.
The projection display device according to Patent Document 1 includes: a liquid crystal panel for display; a projection optical system for enlarging and projecting the image formed by the liquid crystal panel on a screen; a driving voltage generator; and a shifting means which is made up of a liquid crystal panel for polarization direction control and a quartz plate, arranged between the liquid crystal panel for display and the projection optical system and driven by the driving voltage supplied from the driving voltage generator.
The shifting means is one that shifts the optical path by use of the double refraction phenomenon of a quartz plate. Specifically, among the light that vertically enters the quartz plate, light of the first polarization (normal light) passes as it is through the quartz plate without being refracted, so that the incident optical path coincides with the exiting optical path. On the other hand, light of the second polarization (abnormal light) is refracted by the quartz plate, so that the exiting optical path is shifted relative to the incident optical path. This relationship between the normal light and the abnormal light is used to control optical path shifting.
The liquid crystal panel for display supplies light of the first polarization to the liquid crystal panel for polarization direction control.
In a state in which a driving voltage is supplied to the liquid crystal panel for polarization control, light of the first polarization passes as it is through the liquid crystal panel for polarization control and enters the quartz plate. In this case, no shifting of the optical path takes place.
On the other hand, in a state in which no driving voltage is supplied to the liquid crystal panel for polarization control, light of the first polarization passes through the liquid crystal panel for polarization control, but the polarization of light is rotated 90 degrees as the light passes therethrough. As a result, the light that passed through the liquid crystal panel for polarization control becomes light of the second polarization and then enters the quartz plate. In this case, a shift of the optical path takes place.
The original image having twice the number of pixels of the liquid crystal panel for display is decomposed into two images I1 and I2 by thinning out every other pixels in the horizontal direction, whereby images I1 and I2 are displayed by the liquid crystal panel for display in a time-divisional manner. In a period during which image I1 is displayed, the driving voltage is supplied to the liquid crystal panel for polarization control, whereas in a period during which image I2 is displayed, supply of the driving voltage to the liquid crystal panel for polarization control is suspended.
On the screen, the projected image of image I1 and the projected image of image I2 are displayed in a time-divisional manner. The projected image of image I2 is displayed at the position shifted in the horizontal direction by ½ pixel pitch relative to the projected image of image I1. By setting display cycle of images I1 and I2 shorter than the afterimage duration of the human eyes, the superimposed image of the projected images of images I1 and I2 can be observed. This observed image (the superimposed image of images I1 and I2) has a pixel count equivalent to that of the original image.